Unit cell U-plate-fin crossflow heat exchanger

ABSTRACT

The invention recites a heat exchanger for the exchange of heat between an internal fluid and an external fluid comprising at least two heat exchange cells. Each heat exchange cell includes a first plate having an outer surface, raised peripheral edges, an inlet aperture, an outlet aperture, and a heat exchange area extending between the inlet aperture and the outlet aperture. Each cell further includes a second plate including raised peripheral edges, an inlet aperture, an outlet aperture, and a heat exchange area extending between the inlet aperture and the outlet aperture. The inlet aperture of the first plate is aligned with the inlet aperture of the second plate to define a cell inlet and the outlet aperture of the first plate is aligned with the outlet aperture of the second plate to define a cell outlet. The heat exchange area of the first plate is aligned with the heat exchange area of the second plate to define an internal U-shaped flow path and the raised peripheral edges of the first plate connect to the raised peripheral edges of the second plate to substantially enclosing the U-shaped flow path between the first and second plate. An internal finned member is disposed within the internal U-shaped flow path and is attached to one of the first and second plates and an external finned member is connected to the outer surface of the first plate.

BACKGROUND AND SUMMARY OF THE INVENTION

[0001] The present invention relates to combustion turbine engines, and particularly to recuperated microturbine engines. More particularly, the present invention relates to recuperated microturbine engines employing plate-fin recuperators.

[0002] Recuperators are heat exchangers used to transfer heat from a hot fluid to a cold fluid. In the case of microturbine engines, the hot fluid is generally turbine exhaust gas while the cold fluid is generally compressed air exiting a compressor. The recuperator preheats the compressed air prior to combustion to improve the overall efficiency of the engine.

[0003] To maximize the efficiency of the engine, it is desirable to use the most effective recuperator possible. To that end, counterflow plate-fin type recuperators are often employed. However, counterflow plate-fin recuperators require inlet manifolds and outlet manifolds spaced apart from one another, increasing the complexity of the heat exchanger. In addition, the spaced apart manifolds reduce the amount of area that can be used for efficient heat exchange.

[0004] Crossflow heat exchangers are known to be less effective than counterflow heat exchangers. To improve crossflow heat exchanger effectiveness, one of the flows can make two or more passes across the other flow. One way to produce a multi-pass crossflow heat exchanger is to provide a U-shaped path for one of the flows. Tube-type heat exchangers that employ U-shaped tubes are known.

[0005] Thus, according to the present invention a heat exchanger for the exchange of heat between an internal fluid and an external fluid comprises at least two heat exchange cells. Each heat exchange cell includes a first plate having an outer surface, raised peripheral edges, an inlet aperture, an outlet aperture, and a heat exchange area extending between the inlet aperture and the outlet aperture. Each cell further includes a second plate including raised peripheral edges, an inlet aperture, an outlet aperture, and a heat exchange area extending between the inlet aperture and the outlet aperture. The inlet aperture of the first plate is aligned with the inlet aperture of the second plate to define a cell inlet and the outlet aperture of the first plate is aligned with the outlet aperture of the second plate to define a cell outlet. The heat exchange area of the first plate is aligned with the heat exchange area of the second plate to define an internal U-shaped flow path and the raised peripheral edges of the first plate connect to the raised peripheral edges of the second plate to substantially enclosing the U-shaped flow path between the first and second plate. An internal finned member is disposed within the internal U-shaped flow path and is attached to one of the first and second plates and an external finned member is connected to the outer surface of the first plate.

[0006] In preferred embodiments, the heat exchange cells include multiple finned members disposed within the U-shaped flow path to enhance the heat transfer efficiency.

[0007] In another preferred embodiment, the cell inlets align with one another and define an inlet manifold and the cell outlets align with one another to define an outlet manifold. The heat exchanger inlet manifold and outlet manifolds align with one another relative to the external fluid flow to maximize useable heat exchange space for a fixed volume. In addition, two separate and distinct U-shaped flow paths are provided to improve the heat exchanger effectiveness.

[0008] In still other preferred embodiments, the heat exchange cells include a slot disposed between the parallel flow regions of the U-shaped flow path. The slot separates the hottest portions of the heat exchanger area from the coolest portions.

[0009] Additional features and advantages will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The detailed description particularly refers to the accompanying figures in which:

[0011]FIG. 1 is an exploded view of a heat exchange cell of a recuperator in accordance with the present invention;

[0012]FIG. 2 is a cross sectional view taken along line 2-2 in FIG. 1, and illustrating several heat exchange cells;

[0013]FIG. 3 is an exploded view of another embodiment of the heat exchange cell;

[0014]FIG. 4 is a partially broken away top view of the recuperator of FIG. 1;

[0015]FIG. 5 is a partial front view of the recuperator of FIG. 4, taken along line 5-5 in FIG. 4;

[0016]FIG. 6 is a partial perspective view of a cell inlet of the heat exchange cell of FIG. 1;

[0017]FIG. 7 is a cross sectional view taken along line 7-7 in FIG. 6;

[0018]FIG. 8 is a cross sectional view taken along line 8-8 of FIG. 1 and illustrating several heat exchange cells;

[0019]FIG. 9 is a schematic representation of a recuperated microturbine engine in accordance with the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

[0020] A recuperated microturbine engine 10 in accordance with the present invention is illustrated schematically in FIG. 9. The engine 10 includes a compressor 15, a turbine 20, a generator 25, a combustor 30, and a recuperator 35. The turbine 20 includes a rotary element (not shown) that rotates in response to a flow of products of combustion. The turbine rotary element is coupled to a compressor rotary element (not shown) and to a generator rotary element (also not shown) or other driven device. The turbine rotation rotates the compressor rotary element to produce a supply of compressed gas 40, typically air, and further rotates the generator rotary element to produce a current of electricity. There are many different arrangements of microturbine engines 10 including engines that employ two turbines, or engines that drive devices other than generators 25. The present invention functions with any arrangement that uses a turbine 20 and a flow of compressed gas 40. Therefore, the invention should not be limited to the arrangement of FIG. 9.

[0021] In a recuperated microturbine engine 10, the supply of compressed air 40 flows to a recuperator 35 or heat exchanger where it is preheated. The air enters the recuperator 35 through an inlet manifold 45, flows along an internal flow path 50, and exits the recuperator at an outlet manifold 55. The preheated air 60 flows to the combustor 30 where it is combined with a fuel flow 65 and combusted to generate a flow of products of combustion. The products of combustion flow through the turbine 20 imparting rotational energy to the turbine rotary element, which in turn rotates the compressor rotary element to produce the flow of compressed air 40 and rotates the generator rotary element to generate electricity. The products of combustion leave the turbine 20 as a flow of exhaust gas 70. The exhaust gas 70, which is still quite hot, is directed through the recuperator 35 in an external flow path direction 75, allowing heat transfer to the relatively cool compressed air stream 40 flowing along the internal flow path 50. The exhaust gas 70 exits the recuperator 35 and is vented to the atmosphere or further processed as desired. The use of a recuperator 35 in the standard Brayton cycle allows for increased thermal efficiency, with the effectiveness of the recuperator 35 directly effecting the thermal efficiency of the cycle.

[0022] Referring to FIGS. 1 and 2, one construction of a heat exchange cell 80 includes a lower plate 85, an upper plate 90, a plurality of inner fin members 95, two turning region fin members 100, and a plurality of outer fin members 105. The lower plate 85 defines an inlet aperture 110, an outlet aperture 115, heat exchange areas 120, two turning regions 125, and a slot 130. The peripheral edges 135 surrounding the outside of the plates 85, 90 and defining the slots 130 are raised toward the interior of the heat exchange cell 80, as is best shown in FIG. 2. Interior edges 140 surround the inlet aperture 110 and the outlet aperture 115 and are raised away from the interior of the heat exchange cell 80. The peripheral edges 135 and interior edges 140 will be discussed in greater detail below.

[0023] To assemble the heat exchange cell 80 of FIG. 1, inner fin members 95 first attach to the lower or upper plate 85, 90 in the heat exchange area 120. The inner fin members 95, which are generally corrugated pieces of metal, define internal flow channels that guide the flow from the inlet aperture 110 to one of the turning regions 125. Turning region fin members 100 attach to the lower or upper plates 85, 90 at either end to turn the fluid and redirect it toward the outlet aperture 115. Additional inner fin members 95 attach to the lower or upper plate 85, 90 and receive the flow from the turning regions 125. The inner fin members 95 guide the flow to the outlet aperture 115. Thus, the arrangement illustrated in FIG. 1 provides two separate and distinct U-shaped flow paths 145 within the heat exchange cell 80. Each U-shaped flow path 145 includes an outbound flow leg 150, a flow reversing leg 155, and an inbound flow leg 160. The second U-shaped flow path 145 is positioned so that the flow follows a path that is a substantial mirror image of the path followed by the flow within the first U-shaped flow path 145.

[0024] The upper plate 90, which is substantially identical to the lower plate 85, is inverted and positioned relative to the lower plate 85 so that the inlet apertures 110, outlet apertures 115, and slots 130 align with one another. The peripheral edges 135 of the upper plate 90 contact the peripheral edges 135 of the lower plate 85, thereby sandwiching the inner fin members 95 between the plates 85, 90. The peripheral edges 135 are connected to one another utilizing a suitable attachment method (e.g., welding, soldering, brazing, bolting, etc.) to seal all but the inlet apertures 110 and the outlet apertures 115. The aligned inlet apertures 110 define a cell inlet 165 where fluid flow enters the two U-shaped flow paths 145 and the aligned outlet apertures 115 define a cell outlet 170 where fluid flows out of the two U-shaped flow paths 145. The cell inlet defines an axis 11-11 that extends through the centers of the inlet apertures 110 from the lower plate 85 to the upper plate 90. The cell outlet defines an axis 12-12 that extends through the centers of the outlet apertures 115 from the lower plate 85 to the upper plate 90. The cell inlet and outlet axes are substantially parallel to each other and together define a plane that is substantially perpendicular to the flow channels defined by the inner fin member 95.

[0025] The aligned slots 130 separate the outbound flow legs 150 and the inbound flow legs 160 of the U-shaped flow paths 145. The exhaust gas 70 flowing through the recuperator 35 along exhaust gas flow direction 75 is at its hottest temperature when adjacent the inbound flow leg 160 and at its coolest temperature when adjacent to the outbound flow leg 150. In response to these temperature differences and the thermal gradients created thereby, the heat exchange area 120 supporting the inbound flow leg 160 of the U-shaped flow paths 145 will have a tendency to thermally expand to a greater extent than the heat exchange area 120 supporting the outbound flow leg 150 of the U-shaped flow path 145. This differential thermal expansion can result in large thermal stress levels and structural failure if left unchecked. The slot 130 separates the outbound flow legs 150 from the inbound flow legs 160 and allows the legs 150, 160 to substantially independently expand, thereby reducing the thermal stress within the heat exchange cells 80.

[0026] Outer fin members 105 attach to the outer surface 162 of the heat exchange cell 80 to define external flow channels that guide the flow of exhaust gas 70 around the outside of the heat exchange cell 80 and define the flow path 75. The outer fin members 105 are generally corrugated metal pieces like the inner fin members 95, however the outer fin member corrugations are turned approximately ninety degrees with respect to the corrugations of the inner fin members 95. Thus, the outbound flow leg 150 and inbound flow leg 160 of the U-shaped flow paths 145 and the external flow path direction 75 are arranged in a generally crossflow orientation. While the construction of FIG. 1 shows outer fin members 105 on both the top and bottom outer surfaces 162 of the heat exchange cell 80, other constructions may use outer fin members 105 on only one of the top and bottom surface 162.

[0027] Slot 130 is open to the exhaust gas flow and permits, the exhaust gas to travel vertically and into flow paths between different adjacent heat exchange cells 80. This vertical flow is minimal due to the substantially even distribution of exhaust gas 70 and the substantially equal exhaust gas pressures between adjacent heat exchange cells 80. To prevent leakage out of the top and bottom of the slot 130, a housing or duct 163 (shown partially in FIG. 5) surrounds the stack of heat exchange cells 80. The duct 163 guides the flow of exhaust gas 70 into the recuperator 35 and simultaneously prevents leakage through the top and bottom of the stacked heat exchange cells 80. The duct 163 also prevents exhaust gas from escaping from the recuperator 35 before it flows across the entire U-shaped flow path 145 of the recuperator 35.

[0028]FIG. 2 better illustrates the peripheral edges 135 and the inner fin members 95 of several heat exchange cells 80. FIG. 2 is a cross sectional view of FIG. 1 taken along line 2-2 with three heat exchange cells 80 stacked on top of one another along a stackwise direction 13-13. It should be understood that FIG. 2 shows only three heat exchange cells 80 for clarity, and that many heat exchange cells 80 would be stacked on top of one another to complete a recuperator 35. The inner fin members 95 illustrated in FIG. 2 have a substantially sinusoidal cross-section. FIG. 7 illustrates an inner fin member 95 having a square wave cross-section, rather than the sinusoidal section shown in FIG. 2. Fin members 95, 100, 105 with many other cross sections will also function with the invention (e.g., triangle-wave pattern, D-shape, W-shape, etc.). In fact, the present invention will function with any shape fin members 95, 100, 105 because the shape is likely to only influence the overall effectiveness of the recuperator.

[0029] The peripheral edges 135 of the upper plate 90 contact those of the lower plate 85 to facilitate connection of the plates 85, 90 and to substantially enclose the U-shaped flow path 145. The peripheral edges 135 include an attachment portion 175 and an angled portion 180. The angled portion 180 extends from the heat exchange area 120 to the attachment portion 175, which is generally parallel to the heat exchange area 120 of the plate 85, 90. The attachment portions 175 of the upper plate 90 and lower plate 85 contact one another and provide a convenient attachment location around the periphery of the heat exchange cell 80 and around the inside border of the slot 130. Once sealed, the cell inlet 165 and the cell outlet 170 become the only entry and exit points to the U-shaped flow path 145. The actual shape of the peripheral edges 135 is not critical to the function of the invention. Therefore, other shapes (e.g., Z-shaped, L-shaped, S-shaped, etc.) are contemplated and will function with the invention so long as they provide a convenient means of spacing the upper plate 90 heat exchange area 120 from the lower plate 85 heat exchange area 120 while attaching the plates 85, 90 to one another. For example, FIG. 5 illustrates a construction of a recuperator 35 in which S-shaped peripheral edges 135 are employed.

[0030] Turning to FIG. 3, an alternative construction of a U-shaped heat exchange cell 80A in accordance with the present invention is shown, wherein similar components are labeled with similar reference numerals and the extension “A”. The heat exchange cell 80A includes an upper plate 90A, a lower plate 85A, two inner fin members 95A, a turning fin member 100A and four outer fin members 105A. The upper plate 90A and lower plate 85A are substantially similar to the upper plate 90 and lower plate 85 of FIG. 2 with the exception of the inlet and outlet aperture 110A, 115A locations. Instead of positioning the apertures 110A, 115A away from the ends of the plates 85A, 90A to provide two distinct U-shaped paths 145A, the present construction positions the inlet and outlet apertures 110A, 115A near one of the ends. The present construction thus provides a single U-shaped flow path 145A. Each plate 85A, 90A includes a heat exchange area 120A, a turning region 125A, peripheral edges 135A and apertures 110A, 115A having interior edges 140A. The peripheral edges 135A of the upper plate 90A attach to the peripheral edges 135A of the lower plate 85A as described with respect to previous constructions to define a U-shaped flow path 145A extending from the inlet aperture 110A to the outlet aperture 115A. The inner fin members 95A and the turning fin member 100A are sandwiched between the plates 85A, 90A and guide the flow along the U-shaped path 145A while improving the effectiveness of the heat exchange cell 80A. The outer fin members 105A attach to the outer surface 162A of the heat exchange cell 80A to guide the flow of exhaust gas 70 across the U-shaped flow path 145A and improve the effectiveness of the heat exchange cell 80A.

[0031]FIG. 4 is a top view of a recuperator 35 in accordance with the present invention, better illustrating the fin member 95, 105 orientations. The inner fin members 95 positioned within the individual heat exchange cells 80 extend generally from left to right to define the internal flow paths 50. The outer fin members 105 positioned on the outer surfaces 162 of the individual heat exchange cells 80 extend generally from front to back and define the direction of flow of exhaust gas 75. Thus, the heat exchanger of FIG. 4 includes four distinct crossflow heat exchange areas 120. The slot 130 separates the heat exchange areas 120 supporting the outbound flow leg 150 from the areas supporting the inbound flow leg 160 and the inlet manifold 45 and outlet manifold 55 separate the heat exchange areas 120 of the two U-shaped flow paths 145 from one another.

[0032] The turning regions 125 also perform some heat transfer and add to the overall effectiveness of the recuperator 35. In fact, as the compressed air makes the turn in the turning regions 125, it is closer to the more effective counterflow heat exchanger model.

[0033]FIG. 4 also illustrates the alignment of the inlet and outlet manifolds 45, 55 relative to the direction of flow of exhaust gas 75. By aligning the inlet and outlet manifolds 45, 55 the effective heat exchange area for a fixed length recuperator 35 is maximized, thereby improving the overall effectiveness of the recuperator 35. The inlet and outlet manifold 45, 55 can be located at one end of the recuperator 35A as illustrated in FIG. 3 to maximize the useable length of a single flow U-shaped recuperator 35A. However, the multiple path recuperator 35 is preferred, as it allows for reduced flow velocities within the U-shaped flow paths 145, thereby improving the heat exchanger performance and reducing the pressure drop of the gas flowing through the internal flow path 50 (defined by the outbound flow leg 150, flow reversing leg 155, and the inbound flow leg 160).

[0034] Turning to FIGS. 6 and 7, a perspective and end view of a cell inlet 165 in accordance with the present invention better illustrate the peripheral edges 135 and the aperture interior edges 140. The heat exchange area 120 of the plates 85, 90 supports the outer fin members 105 as shown in FIG. 6. The peripheral edges 135 extend from the heat exchange area 120 toward the interior of the heat exchange cell 80. The interior edges 140, on the other hand, extend from the heat exchange area 120 of the plate 85, 90 away from the interior of the heat exchange cell 80. This arrangement allows each heat exchange cell 80 to sandwich an inner fin member 95 between the heat exchange areas 120 of the upper plate 90 and lower plate 85 as shown in FIG. 7. In addition, the raised interior edges 140 provide for sufficient space between adjacent heat exchange cells 80 to accommodate one or more outer fin members 105 as shown in FIG. 6.

[0035]FIG. 8 illustrates the interior edges 140 of adjacent cell inlets 165 attached to one another in a manner similar to that described above with regard to the peripheral edges 135. The interior edges 140 contact one another, thereby providing sufficient space between the adjacent heat exchange cells 80 for the outer fin members 105. Like the peripheral edges 135, any suitable attachment method can be used, however welding is preferred. In other constructions (not shown), support members located away from the inlet and outlet manifolds 45, 55 provide additional support to the adjacent heat exchange cells 80. The support members attach to adjacent heat exchange cells 80 to maintain the desired gap between adjacent heat exchange cells 80, while still allowing free expansion and contraction in response to temperature changes.

[0036] It should be noted that the figures contained herein are meant to further clarify the reader's understanding of the invention. To that end, many features are exaggerated or shown out of scale for the sake of clarity. For example, the plates 85, 90 are shown as having a substantial thickness when compared to the fin members 95, 105. In practice, the plates 85, 90 as well as the fin members 95, 105 would be as thin as practicable to facilitate more rapid heating and improved heat transfer. Therefore, the drawings should not be interpreted as limiting the scope of the invention in any way.

[0037] Although the invention has been described in detail with reference to certain preferred embodiments, variations and modifications exist within the scope and spirit of the invention as described and defined in the following claims. 

What is claimed is:
 1. A heat exchanger comprising at least two heat exchange cells for the exchange of heat between an internal fluid and an external fluid, each heat exchange cell comprising: a first plate having an outer surface, raised peripheral edges, an inlet aperture, an outlet aperture, and a heat exchange area extending between the inlet aperture and the outlet aperture; a second plate including raised peripheral edges, an inlet aperture, an outlet aperture, and a heat exchange area extending between the inlet aperture and the outlet aperture, the inlet aperture of the first plate aligned with the inlet aperture of the second plate to define a cell inlet, the outlet aperture of the first plate aligned with the outlet aperture of the second plate to define a cell outlet, the heat exchange area of the first plate aligned with the heat exchange area of the second plate to define an internal U-shaped flow path, and the raised peripheral edges of the first plate connected to the raised peripheral edges of the second plate to substantially enclose the U-shaped flow path between the first and second plates; an internal finned member disposed within the internal U-shaped flow path, and attached to one of the first and second plates, the internal finned member defining flow channels; and an external finned member connected to the outer surface of the first plate.
 2. The heat exchanger of claim 1, wherein the heat exchange cells are stacked on top of one another and the external finned member is disposed between adjacent heat exchange cells, the external finned member defining flow channels oriented substantially perpendicular to the flow channels of the internal finned member.
 3. The heat exchanger of claim 1, wherein each cell inlet defines an inlet axis and each cell outlet defines an outlet axis, the inlet and outlet axes defining a plane substantially perpendicular to the internal flow channels.
 4. The heat exchanger of claim 1, wherein each of the heat exchange cells includes a turning region receiving a flow of the internal fluid from the internal finned member and redirecting the flow in substantially the opposite direction to the cell outlet.
 5. The heat exchanger of claim 1, wherein the first and second plates further define a slot within each plate, the slots having raised peripheral edges connected to one another to at least partially enclose the U-shaped flow path.
 6. The heat exchanger of claim 1, wherein the heat exchange area of the first plate and the heat exchange area of the second plate align with one another to define two U-shaped flow paths providing two distinct flow paths that substantially mirror one another.
 7. The heat exchanger of claim 6, wherein the cell inlet and the cell outlet are disposed between the two U-shaped flow paths.
 8. A heat exchanger for the exchange of heat between an internal fluid and an external fluid, the heat exchanger comprising: a plurality of heat exchange cells stacked in a stackwise direction, each cell including first and second plates, each plate having peripheral edges raised in a first direction, an inlet aperture having internal edges raised in a second direction substantially opposite the first direction, an outlet aperture having internal edges raised in the second direction, and a heat exchange area extending between the inlet aperture and the outlet aperture, the second plate being inverted with respect to the first plate such that the inlet aperture of the first plate aligns with the inlet aperture of the second plate to define a cell inlet, the outlet aperture of the first plate aligns with the outlet aperture of the second plate to define a cell outlet, the heat exchange area of the first plate aligns with the heat exchange area of the second plate to define an internal U-shaped flow path, and the peripheral edges of the first plate connect to the peripheral edges of the second plate to substantially enclose the U-shaped flow path; wherein the inlet internal edges of adjacent heat exchange cells align with and are connected to one another to define an inlet manifold and the outlet internal edges of adjacent heat exchange cells align with and are connected to one another to define an outlet manifold.
 9. The heat exchanger of claim 8, wherein the U-shaped flow path further includes a turning region, a first flow leg extending in a first flow direction from the cell inlet to the turning region, and a second flow leg extending in a second flow direction from the turning region to the cell outlet, the second flow direction substantially opposite the first flow direction.
 10. The heat exchanger of claim 9, further comprising a first internal finned member disposed within the first flow leg, a second internal finned member disposed within the second flow leg, and a turning finned member disposed within the turning region.
 11. The heat exchanger of claim 8, wherein the heat exchange cells include a top surface and a bottom surface and wherein a first external finned member is connected to one of the top surface and bottom surface.
 12. The heat exchanger of claim 11, wherein each cell inlet defines an inlet axis extending from the first plate to the second plate and each cell outlet defines an outlet axis extending from the first plate to the second plate, the inlet and outlet axes defining a plane substantially parallel to the external flow channels.
 13. The heat exchanger of claim 8, wherein the first and second plates further define a slot within each plate, the slots having raised peripheral edges connected to one another to at least partially enclose the U-shaped flow path.
 14. The heat exchanger of claim 8, wherein the internal U-shaped flow path within each heat exchange cell is a first internal U-shaped flow path, and wherein the first plate and the second plate further define a second internal U-shaped flow path that is a substantial mirror image of the first U-shaped flow path.
 15. A recuperated combustion turbine engine comprising: a compressor operable to produce a flow of compressed gas; a combustor receiving the flow of compressed gas and combusting it with a flow of fuel to produce a flow of products of combustion; a turbine receiving the flow of products of combustion and discharging an exhaust gas, the turbine operable under the influence of the flow of products of combustion therethrough; and a plate-fin heat exchanger having a plurality of heat exchange cells stacked in a stackwise direction, each heat exchange cell including first and second plates having raised peripheral edges connected to one another to define an inner U-shaped flow path, a cell inlet, and a cell outlet, each heat exchange cell including a finned member connected to one of the first and second plates and disposed within the inner U-shaped flow path to define internal flow channels; wherein the flow of exhaust gas passes through the heat exchanger along a first flow path between adjacent heat exchange cells and the flow of compressed gas passes through the heat exchanger along the U-shaped flow path within the heat exchange cells.
 16. The engine of claim 15, wherein each U-shaped flow path further includes a turning region, a first flow leg extending in a first flow direction from the cell inlet to the turning region, and a second flow leg extending in a second flow direction substantially opposite the first flow direction from the turning region to the cell outlet.
 17. The engine of claim 16, wherein the finned member is a first finned member disposed within the first flow leg, each heat exchange cell further including a second internal finned member disposed within the second flow leg, and a turning finned member disposed within the turning region.
 18. The engine of claim 15, wherein the heat exchange cells include a top surface and a bottom surface and wherein a first external finned member is connected to one of the top surface and bottom surface to define external flow channels substantially perpendicular to the internal flow channels.
 19. The engine of claim 15, wherein the cell inlets of adjacent heat exchange cells are aligned and attached to one another to define an inlet manifold and cell outlets of adjacent heat exchange cells are aligned and attached to one another to define an outlet manifold.
 20. The engine of claim 15, wherein each cell inlet defines an inlet axis and each cell outlet defines an outlet axis, the inlet and outlet axes defining a plane substantially perpendicular to the internal flow channels.
 21. The engine of claim 15, wherein the first and second plates further define a slot within each plate, the slots having raised peripheral edges connected to one another to at least partially enclose the U-shaped flow path.
 22. The engine of claim 15, wherein the U-shaped flow path within each heat exchange cell is a first U-shaped flow path, and wherein the first plate and the second plate define a second U-shaped flow path that is a substantial mirror image of the first U-shaped flow path. 